1. Field of the Invention
The present invention relates to a hub unit, a method for manufacturing the hub unit and a method for transporting the hub unit.
2. Related Art
Conventionally, hub units for mounting a wheel and a brake disc are used on vehicles such as automobiles.
When vehicles such as automobiles are transported by cargo-trains or boats etc., minute vibrations are subjected to hub units mounted on the vehicles, whereby fretting wear is generated, producing wear dust, this producing false brinelling on raceway portions. Then, wear dust is oxidized to become iron oxide, and iron oxide so produced promotes the wear further, resulting in expansion of false brinelling.
As preventive measures, clearance filling is implemented. In addition, a technique is disclosed in which a high-frequency heat treatment is applied to a portion on a surface area of a hub body which lies from an inner ring raceway surface to a root portion of a flange so as to form a hardened portion thereon (JP-A-11-51064).
When a vehicle equipped with a hub unit in which false brinelling was generated by fretting wear during transportation is run, abnormal noise is generated. While false brinelling affects the life of a hub unit, such a clearance filling by itself cannot suppress sufficiently the occurrence of fretting wear. Further, the hardening treatment as suggested in JP-A-11-51064 calls for an increase in production costs.